RBP4 and acute kidney injury: We compared aptamer-based measurements with the corresponding Meso Scale Discovery immunoassay-based protein measurements of proteins found to be significantly associated with AKI sub-phenotypes (REG3A, MMP2, HAMP, RBP4, PRDX6) and candidate urinary biomarkers of kidney injury, such as KIM-1, NGAL, EGF, IL-18 and Ang-2 (Table S4).